Bathroom extractor fan - is fuse necessary?

[stagman]

I am having a new bathroom installed and an extractor fan is required. The supply to the bathroom is on the upstairs lighting circuit from an RCD protected 5A MCB in the consumer unit and the fan will be fed from this circuit. There is a 3 pole fan isolator switch outside the bathroom but the extractor fan instructions say it should have a 3A fuse. Adding an FCU to feed just the bathroom makes it all over complicated. Since the whole lot is fed from a 5A MCB, would this not make the addition of a 3A fuse unnecessary?

 

[Electrifying]

It's not a case of 'necessary' or 'unneccesary' - additional 'manufacturer instructions' need to be complied with - at the very least, you'll void any warranty/guarantee that the unit comes with if you don't comply.

 

[sherlockholmes]

Well no, 5A overcurrent protection and 3A overcurrent protection aren't the same thing. 3 isn't 5.

I doubt it would be a problem, they aren't going to send the fan installation inspectors round if you make a claim under warranty and it's not going to draw more than 3 amps unless a fault develops. If a fault develops that results in the fan drawing more than 3 but less than 5 amps, perhaps fire, death and destruction will fall from the skies and the four horsemen of the apocalypse will ride. It seems rather unlikely, i'd put the recommended fuse on anyway.

 

[ericmark]

I would agree with sherlockholmes. Likely because the preferred fuse sizes are 3A and 13A the 3A has been selected. And likely the 6A MCB will give the same protection.

However unless you can get the manufacturer to confirm this then if you want to follow the rule book and get a completion certificate issued likely you will need to fit a 3A fuse.

There are some considerations.
1) FCU's can be locked off.
2) If the fan fails then it may take out fuse without plunging you into darkness.

ELI for 3A BS 1362 fuse = 16.4 ohms
ELI for 6A type B MCB = 7.67 ohms

No one is able to say other than the manufacturer don't worry a 6A MCB is fine. Even if it is. So really no point asking on here. Only person you can ask is manufacturer.

 

[EFLImpudence]

I don't disagree with anything that has been said,

However, does anyone know why manufacturers state such fuse ratings when they have little relation to the rating of the appliance?
E.g. most extractor fans are 1A or even less.

Oven manufacturers who state 16A even though they may be connected with 6mm² cable.

Just interested.

 

[stagman]

Thanks for the replies. Looks like I will have to put in the extra FCU for the sake of a 2A reduction, with more cable junctions comes possible future weaknesses.

 

[EFLImpudence]

I take it that's a "no" then.

With regard to extractor fans, if the manufacturers are so worried about there equipment failing and wreaking havoc with someone's house why don't THEY fit a 1amp (or smaller) fuse inside the fan instead of compelling us to fit an inappropriate 3amp in a large extra box on the wall.

Is it likely because of the "may contain nuts" syndrome that abounds nowadays?

 

[stagman]

I take it that's a "no" then.

With regard to extractor fans, if the manufacturers are so worried about there equipment failing and wreaking havoc with someone's house why don't THEY fit a 1amp (or smaller) fuse inside the fan instead of compelling us to fit an inappropriate 3amp in a large extra box on the wall.

Is it likely because of the "may contain nuts" syndrome that abounds nowadays?

You are quite right - the electronics industry fuses everything individually with an appropriate fuse.

It's all part of the backyard clearing exercise for when the lawsuits come along.